I’m not entirely sure about what you mean by flowcharts. I guess these are either the movement of materials in a sequence involved with logistics or a diagram representing a conversation e.g. on the phone:

A: Answer giving your name and the name of your company

B: Greet A and explain why you are calling

Etc.

I am not aware of any course books that contain only or mostly examples of flowcharts.

For the example of logistics, you could ask your students to produce their own flowcharts; they might have flowcharts themselves or they could draw one. If it is individualised in this way, it will be more meaningful to students. Also flowcharts can vary from one company to another, so students will describe and work on the method they are familiar with.

As for flow charts for dialogues, you can find many examples of these in business course books; especially those for practising speaking. You could try the International Express series.